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H2oNet Pumps system pressure

Hi,

I had a model with a tank and using 3 pumps for supply a community with water. When the pressure drops to 20 psi the system had another pump for fire.
I model the 3 pumps but How I can model this system with the 3 pumps and setup minimum pressure to activate the fourth pump for fire supply.

You could simply use a control statement (either Simple control or a rule based control) to turn the 4th pump on when the pressure drops below a specified limit. You will need to decide if 20 psi is the best choice for the pressure and which location will be used for the pressure control point. Generally, most models are simply set up to replicate the actual controls used in the field so generally you would simply need to find out how the real pump is controlled and create a control statement for the 4th pump to replicate that.

The choice of using simple vs rule based controls is important as well as simple controls are evaluated during steady state runs and generally would turn the fire pump on as part of a fireflow run. However, simple controls can lead to a model not-converging if the "on" and "Off" simple controls fight to turn the pump on and off during each trial while iterating to get model convergence. So use caution of using a pressure "ON" statement like 'pump 1 on if the pressure at location X < 20 psi' and then you have an "Off" control like 'pump 1 off if the pressure at location X > 20 psi' as the pump woudl turn on and then increase the pressure above 20 psi and then also turn off.

Rule based controls have a time delay built in which increases model stability, but these are not evaluated under Steady State runs and generally would not turn on for any fireflow analysis.